This invention relates to triazine compounds and their use in the manufacture of electro-luminescent, electronic and liquid crystal devices. In particular the present invention is concerned with triazine derivatives which are capable of exhibiting a nematic discotic liquid crystal phase, a columnar liquid crystal phase and/or a columnar crystalline phase.
Mesogenic compounds which are capable of exhibiting a discotic columnar liquid crystalline phase are known as electric charge carriers for use in electro-luminescent devices. For example, D. Adam et al, Nature, volume 371, Sep. 8, 1994, pages 141 to 143 disclose that 2,3,6,7,10,11-hexahexylthiotriphenylene is capable of exhibiting a discotic liquid crystal phase and that a highly ordered helical columnar phase of this compound forms by cooling an isotropic liquid melt thereof via the discotic liquid crystal phase. Compounds of this type are suitable for transport of holes. DE-A-4343412 discloses discotic liquid crystal charge transport compounds based on a variety of molecules including triphenylene, phthalocyanine, tricycloquinazoline, perylene, decacyclene and porphyrine. DE-A-4343412 also discloses calamitic liquid crystal compounds based on oxadiazole, thiadiazole, biphenyl, terphenyl, quaterphenyl, stilbene, pyrimidine and oxazoline. DE-A-4325238 also discloses organic charge transporting compounds having liquid crystal properties based on tricycloquinazoline. C. Nuckolls et al, J. Am. Chem. Soc., 1996, volume 118, pages 3767 to 3768 and A. J. Lovinger et al, J. Am. Chem. Soc. 1998, volume 120, pages 264 to 268 describe a highly aggregated fibrous columnar phase of a coloured helicene derivative that may be especially useful for charge transport due to the apparently strong interaction of neighbouring molecular cores in the columnar stack.
D. Goldmann et al (Liquid Crystals, 1996, Vol 21, No 5, 619-623) disclose sheet-shaped mesogens based on 2,4,6-triarylamino-1,3,5-triazine, more specifically 2,4,6-tris(3,4-dialkoxyphenylamino)-1,3,5-triazines. In such compounds, the aryl substituent is connected to the triazine ring via a secondary amino group. The free hydrogen on the secondary amino group is quite reactive and so there would be a tendency for the molecule to decompose, particularly under the conditions experienced in use in electroluminescent devices.
It is an object of the present invention to provide a novel class of triazine compounds which have an electron-deficient central unit that favours transport of negative charges (electrons), which are not coloured and therefore do not absorb light, and which are chemically relatively unreactive since they do not bear reactive groups such as xe2x80x94NHxe2x80x94, and so are less susceptible to unwanted decomposition.
According to the present invention, there is provided a class of triazine compounds of the general formula: 
wherein Ar, Arxe2x80x2 and Arxe2x80x3 are aromatic moieties and are the same or different; each of R1, R1xe2x80x2, R1xe2x80x3 to Rn, Rnxe2x80x2, Rnxe2x80x3 (hereinafter sometimes simply referred to as xe2x80x9cgroups Rxe2x80x9d), which may be the same or different, is an elongated flexible, at least partly aliphatic chain such as to impart liquid-crystalline or columnar crystalline properties to the compound; and xe2x80x94(R1, . . . , Rn), xe2x80x94(R1xe2x80x2, . . . , Rnxe2x80x2) and xe2x80x94(R1xe2x80x3, . . . , Rnxe2x80x3) indicate that there are up to n, nxe2x80x2 and nxe2x80x3 substituent groups R on the respective Ar, Arxe2x80x2, Arxe2x80x3 moieties, where n, nxe2x80x2 and nxe2x80x3 are integers which do not exceed the number of available substituent positions on the respective Ar, Arxe2x80x2, Arxe2x80x3 moieties.
Some of the compounds of the present invention are capable of exhibiting a columnar liquid crystal phase or a columnar soft crystalline phase which is advantageous in electro-luminescent devices due to the good charge transport properties along the director direction and the lack of pronounced grain boundaries between domains such as known from rigid crystals. Especially advantageous are those compounds of the present invention which exhibit highly ordered (soft crystalline) columnar phases such as reported by Lovinger et al (supra) and Adam et al (supra) but not by Goldmann et al (supra), due to enhanced transport in more ordered systems. An example of such a compound is 2,4,6-tris-(3,4-dinonyloxyphenyl)-1,3,5-triazine.
Furthermore, some of the compounds of the present invention are mesogenic compounds which are capable of exhibiting a discotic nematic phase at room temperature which is advantageous for use in liquid crystal devices due to their elastic properties compared to standard (calamitic) nematics, eg for flexoelectric cholesteric displays, and due to their optical and alignment properties, eg for optical compensation layers to enhance the viewing angle dependence of displays. Such compounds may be those in which R is an acyloxy group such as a (C5 to C8)acyloxy group.
The above property of being capable of exhibiting a columnar liquid crystal phase, columnar soft crystalline phase and/or a discotic nematic phase may be exhibited by the compound either in its pure state or when in admixture with one or more other such triazine compounds or when in admixture with one or more other compounds or both where the amount exceeds 20 wt % (more typically  greater than 50 wt %) of the mixture. Such one or more other compounds may be one or more other triazine compounds according to the present invention.
The aromatic moiety in each of Ar, Arxe2x80x2 and Arxe2x80x3 may be a single or multiple ring (fused and/or unfused) monoaromatic or heteroaromatic moiety. Conjugation of the aromatic unsaturation in Ar, Arxe2x80x2 and Arxe2x80x3 with the central triazine group, combined with the planarising action of the electronic attraction of the nitrogens and inner hydrogens in the above formula, effectively holds the three aromatic and the central triazine group in a planar (discotic) form, thereby facilitating the formation of columnar and nematic phases.
Compounds of the above-defined type have an electron-deficient central unit, because they incorporate nitrogens in the aromatic ring, and thereby facilitate the production of a liquid-crystalline and/or columnar electron transport layer for use in electro-luminescent devices. Such compounds are most preferably colourless, contain no chemically reactive groups such as eg xe2x80x94NHxe2x80x94 or xe2x80x94OH and exhibit a liquid crystalline and/or columnar phase at room temperature. The compounds of D. Goldmann et al. (supra) contain xe2x80x94NHxe2x80x94 groups.
JP-A-7-157473 and JP-A-8-199163 disclose triazine guiding materials for use in electron-transport in electro-optical devices. However, in such triazine compounds, substituent groups to the triazine contain benzoxazole, benzthiazole, benzimidazole or arylamino moieties and are not capable of exhibiting a liquid crystalline and/or columnar phase because flexible chains are lacking and, in some cases, because heteroatoms in the inner positions or the three aromatic substituents favour high torsion angles between the triazine and the substituent rings.
Some of the compounds of the present invention are rare in being discotic nematics, ie nematics with a negative birefringence. For example, 2,4,6-tris-(3,4-diacyloxyphenyl)-1,3,5-triazines where the acyl group is pentanoyl, hexanoyl, heptanoyl or octanoyl are such compounds. Known discotic nematic compounds are either very large and therefore the phase is highly viscous, or of poor chemical inertness or have very high clearing points. The compounds of D. Goldmann et al. (supra) are not reported as possessing a nematic phase.
Additionally, and especially if at least one of the groups R is polymerisable, the compound of the present invention may be a polymerisable mesogen which has potential use, for example, in the manufacture of optical viewing angle compensation films for electro-optical displays.
Preferably, the groups R are independently selected from alkyl, alkyloxy, alkylthio, alkylamino, acyl, acyloxy, acylthio, acylamino, alkyloxycarbonyl and their alkenyl and alkynyl equivalents, where the alkyl moieties may include heteroatoms and/or further aromatic moieties. It is preferred for each of the groups R to have a carbon chain length of at least about four carbons, preferably about 4 to 20.
In one series of the embodiments, the compound of the present invention has the general formula: 
wherein R1 to R9 are selected from H and the above possibilities for R, provided that at least one of R1 to R3, at least one of R4 to R6 and at least one of R7 to R9 are independently selected from the above possibilities for R. For example, R1, R4 and R7 may be H and the remainder may be R, eg Cnxe2x88x921H2nxe2x88x921COOxe2x80x94 where n is 1 or more, preferably 2 to 20. Cnxe2x88x921H2nxe2x88x921COOxe2x80x94 may be, for example, be n-hexanoyloxy or n-heptanoyloxy. These compounds can be conveniently produced starting with the known synthesis of triveratryltriazine from veratronitrile, followed by demethylation and esterification, according to the following reaction scheme: 
Analogous methods may be used for preparing the certain of the compounds according to the present invention having the following general formulae: 
wherein R1 to R15 are independently selected from H and R (where R is as defined as in any one of claims 1 to 4), provided that at least one of the substituents on each of the aromatic moieties attached to the triazine ring is independently selected from R, n is 1 to 20 and m is 0 to 20.
The last four mentioned general formulae above contain ethylenic unsaturation and may be UV-polymerised. This is potentially useful for making optical compensation films where a layer of the triaryl-triazine is deposited, for example by spinning, onto a substrate followed by UV-polymerisation to effect cross-linking.
Embodiments of various devices utilising compounds according to the present invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a schematic perspective view of an organic electroluminescent device with columnar hole and electron transport layers,
FIG. 2 is a schematic sectional view showing in more detail the basic structure of an electroluminescent device wherein those parts of the device which are similar to that of FIG. 1 are accorded the same reference numerals,
FIG. 3 is a schematic view of a photovoltaic device incorporating at least one compound according to the present invention,
FIG. 4 is a schematic view of a transistor incorporating at least one compound according to the present invention, and
FIG. 5 is a schematic view of a dual layer device for use in electrophotography, e.g. a photocopier.